1. Field of the Invention
The present invention relates to a lighting device. More particularly, the present invention relates to a lighting device for articles on exhibition, objects of photo shooting, and the like, or a lighting device for illuminating liquid crystal display elements and the like.
2. Description of the Related Art
Conventional light sources for lighting devices such as incandescent lamps and cathode ray tubes have problems with regard to light emission efficiency and life span, and light emitting diodes (LEDs) are expected as future light sources. Light emitted by LEDs is of short wavelength color such as blue or green, and has to be turned into white light when used for illumination. A known way to turn LED light into white light is to mix light emitted by a red LED, light emitted by a blue LED, and light emitted by a green LED. As disclosed in JP 05-152609 A, using a blue LED in combination with a yellow phosphor, typically YAG, to obtain pseudo-white light is a widely practiced method. Most light sources that are called white LEDs employ this method, too. Problems with white LEDs, which have very little green and red components, are that their color-rendering properties are lacking and that it is difficult to adjust their chromaticity. While the problem of the color-rendering properties can be solved by using a near-ultraviolet LED, the package reliability and light emission efficiency of white LEDs are still issues at present.
In the case of an LED package that covers an LED element with resin containing a phosphor, the chromaticity can be adjusted by varying the amount of the phosphor mixed in the resin, but the problem is that the phosphor precipitates before the resin cures, thereby making the actual chromaticity off the intended chromaticity. A solution to this problem has been published in which a phosphor containing portion is divided into multiple members so that a first phosphor containing member with a phosphor localized in some part of its body and a second phosphor containing member with the same localized phosphor are stacked on top of each other, and the chromaticity is adjusted by varying the area ratio of the phosphor that can be seen from the light source (see, for example, JP 2006-332384 A). However, this and similar methods have been designed basically to improve the first run rate in mass production, and are good for a slight color tone adjustment, but not for a drastic color tone adjustment or unlimited control of spectral components.